Allentown Pinfest - you hit northeast, NYC, Philly, Pittsburgh, Baltimore, Wash DC etc... Tons of collectors in the market the show draws from.
Pinball Expo and TPF are also going to be worth your travel buck.
Try one in south, rockies, and west coast then you are hitting new folks at each show - don't just go to 5 shows all in the same state that draw from same people if your show budget it limited - spend a bit more and spread out.
Good luck !